1. Field of the Invention
The present invention relates to an apparatus for driving and controlling a motor which moves (raises and lowers) a movable portion of a vehicle, such as a door glass of a power window apparatus, by the driving force of the motor.
2. Description of the Related Art
A power window apparatus is provided with a motor for raising and lowering a door glass.
Generally, manual switches and an auto-switch are provided at a location near the driver's seat as switches for the power window apparatus.
When the driver operates one of the manual switches, the contact for raising or the contact for lowering is turned on. Upon termination of the operation, the manual switch is automatically returned so that the contact is turned off. Since driving of the motor is continued only when the operation of the manual switch continues, the raising and lowering of the door glass can be stopped halfway.
In an automatic operation mode, once the contact for raising or the contact for lowering of the auto-switch is turned on, driving of the motor is continued until the door glass is completely closed or is completely opened even after the driver releases the auto-switch. When the door glass is completely closed, the movement of the door glass is prevented by the window frame or the like, whereby the drive current of the motor increases. Further, driving of the motor may be stopped when the drive current exceeds a predetermined level, or when an abnormal increase in drive current (hereinafter referred to as "abnormal current") due to the catching of a foreign object on the locus of upward movement of the door glass is detected. In such a system, there is provided a full-closure detecting switch for detecting that the door glass is nearing its full closure position so that a current increase due to a foreign object may be discriminated from a current increase due to the full closure of the door glass. Further, it is possible to reverse the motor for a predetermined period of time when the catching of a foreign object is detected.
However, resistance to the movement of the door glass is effected by the temperature of the environment of the door glass, and the drive current of the motor varies in accordance with variation of the resistance. Namely, since freezing and dew condensation occur at low temperatures (especially, at temperatures near the freezing temperature), the movement of the regulator mechanism becomes dull. Further, the smooth movement of the door glass is hindered by the guide portions for the door glass (such as the window frame, weatherstrips made of rubber, and the like) due to the change in hardness of rubber parts, such as the weatherstrips and the like. Accordingly, it is determined that the detected level corresponds to lock current, which occurs when the door glass is fully closed, or that there is abnormal current, even if the door glass has not been completely closed or no foreign object exists on the locus of movement of the door glass. In this case, a drawback arises in that the motor is erroneously stopped such that the door glass cannot be fully closed in a low temperature state.
To obviate the above-mentioned drawback, a system has been considered in which a threshold value for detecting the abnormal current is set to be relatively high so as to be adapted to low temperatures. In this case, setting of the threshold value becomes difficult because the difference between the drive current of the motor at low temperatures and the motor lock current at ordinary temperatures is extremely small. Further, either at ordinary temperatures or at higher temperatures, there may be cases in which the threshold value becomes higher than the motor lock current. In such cases, the overloaded state of the motor continues.